1. Field of the Invention
The present invention is related to a color correcting apparatus for correcting a color reproduction characteristic of a color input/output appliance, and for converting a color image signal into color image data used to form a color image.
2. Description of the Related Art
In color input/output appliances, corrections are made in accordance with color reproduction characteristics of the respective appliances, and thereafter color signals are inputted, or outputted. FIG. 10 is an explanatory diagram for explaining input signal processing operation by a conventional color image scanner. In this color image scanner, an input process operation 8 is carried out by a color CCD (charge-coupled device). The color CCD color-separates a color image of an original to output the color-separated color image as R (red), G (green), B (blue) signals. In a shading correction process operation 9, the respective levels of the entered R, G, B signals are regulated. Furthermore, in a line correction process operation 10, color shifts (deviation) are corrected which are caused by positional differences in the respective R, G, B color CCDs with respect to the original. In addition, in a color correction process operation 11, a color correction is carried out so as to correct color difference from the image of the original, which are caused by the characteristics of the lamps of the color image scanner and of the color CCDs. In the color correction process operation 11, the inputted R, G, B signals are transformed by way of a transformation matrix of 3-row by 3-column, so that corrected R', G', B' signals are produced. The transformation matrix (transformation coefficient) of 3-row by 3-column is employed so as to correct the color differences between the image and the original, which are caused by the characteristic of the color image scanner. It should be noted that the R', G', B' signals correspond to the NTSC-R, G, B signals ruled in a CRT (cathode-ray tube). The color-corrected R', G', B' signals are outputted to an image processing apparatus connected to the color image scanner.
As explained above, in the case that the color correction is carried out with employment of the linear interpolation by a single transformation matrix, or a single transformation formula, the color correction would become difficult when the characteristic of the color input/output appliance is nonlinear. There is such a problem that when the color correction is carried out with employment of a single transformation formula, this color correction cannot be performed in such a manner that the transformation errors become uniform over the entire color space.
The present invention has an object to provide a color correcting apparatus capable of uniformly reducing transformation errors in an entire color space in response to a characteristic of an input/output appliance, and also capable of executing a color correction in high precision.